In a Friday interview Hillary Clinton was making the point that she finds it difficult to believe people are trying to push her out of the Democratic nomination race. She used the example that her husband Bill was only declared the nominee after a June California primary. Then later in the interview when giving another example of a Democratic nominee in 1968 still in the race by June, she unfortunately used the words "when Robert Kennedy was assassinated." It was a poor choice of words but the example was fine. Some have read a metaphoric message of Obama's political assassination into it, but the timing of that word's use was particulary inappropriate because just days ago, Edward Kennedy was diagnosed with a malignant brain tumor. He is also an important endorser of Obama.
If she had left out the "assassination" part of her example, then there would probably be no fallout from this. The example she was trying to use was valid, but it was too good a sound-bite for news media to not to pounce upon and squeeze every bit of mileage out of. Here's one headline from one U.S. political site, Huffington Post, "Clinton Kennedy Assassination Reference: Raises Bobby's Death To Explain Why She Stays In Race". She's had to do plenty of explaining since.
The RFK reference flap has helped Obama look good. He "took her at her word" when commenting on her explanation. So he gets to look like the understanding, calm and good guy. If he were not so far ahead in the delegate race, the reaction might have been different - it could have been ammunition for him.
After at least 14 months of campaigning in the Democratic nomination process, it's amazing they're still standing on the canvas, and speaking coherently at all so Hillary's misspeaking will be forgiven. Unless there is one last scandal for Obama he will win by decision anyway.